It is known to provide a power-actuated chuck for turning machines such as lathes having a chuck body provided with radially shiftable chuck jaws and wedge or camming members which are linearly displaceable, generally substantially tangentially of the chuck body, i.e. along a secant thereof, and a mechanism for actuating all of the wedge or camming members simultaneously.
Such power-actuated chucks are described, for example, in German printed application (Auslegeschrift) DT-AS No. 2,007,509. In this system, the common actuator for the wedge or camming members is a drive ring which is formed as a gear and which has external toothing engaging or meshing with oppositely extending teeth of the wedge or camming members. A torsion tube is connected to the drive gear and rotatably entrains the latter, the drive tube extending through the hollow spindle of the turning machine to the opposite end of the spindle at which the drive tube is connected to a rotary piston-cylinder arrangement. The piston vanes of the latter are connected nonrotatably with the torque tube and the cylinder housing is connected to an intermediate flange of the spindle end.
In German patent No. DT-PS 2,347,561 and in German patent No. DT-PS 2,004,889, there are described hand-actuated chucks of the aforedescribed general type in which the drive connection between the drive ring and the wedge members includes a pin for each of the wedge members. A slide block is rotatable on each pin and is radially shiftable in a respective radial groove of the drive ring.
In all of these conventional or prior-art chucks, the release of the jaws and the clamping and disengagement strokes of the latter require relatively large displacements of the actuating members such that the teeth of the wedging or camming members fully withdraw from the chuck jaws and enable the latter to be changes.
In the power actuated chuck described in German Auslegeschrift (printed application) DT-AS No. 2,007,509, mentioned earlier, however, the requirement for a rotary-piston-cylinder arrangement provides undesirably high capital expenditure because of the nature of the rotary piston and the difficulty in effectively sealing the cylinder housing. Furthermore, such units have been found to be prone to failure.
In every case, moreover, the rotary piston arrangements require special and custom-built structures for the chuck which has rendered the chuck unsatisfactory for many purposes.
Indeed it is known to provide an axial actuator for such a chuck (see German Pat. No. DT-PS 1,059,741 and German Pat. No. DT-AS 2,139,718). However, these systems do not permit rapid displacement of the actuating members. Rapid change or replacement of the chuck jaws is also not possible and hence the prior art chucks have not been found to be satisfactory for numerically controlled machine tools.